Loudspeaker enclosure



Feb. 11, 1958 E. H. slMPsoN LouDsPEAKER ENcLosURE Filed Oct. 26. 1954 aired States Patent O 2,822,884 LOUDSPEAKER ENCLOSURE Edgar H. Simpson, Chicago, lll. Application October 26, 1954, Seria] No. 464,853 Claims. (Cl. 181-31) This invention is concerned generally with the reproduction of sound, and more particularly with an improved enclosure for a loudspeaker.

Up until recent time, little attention has been paid to extremely accurate reproduction of sound. Thus, AM radio and phonograph records generally have reproduced sound only from approximately 100 or 200 C. P. S. up to about 5000 C. P. S. and sometimes a little higher. Obviously, this is only a very small portion of the spectrum which the normal human ear can comprehend, this spectrum running from the order of 2O C. P. S. up to 16,000 or perhaps even 20,000 C. P. S. The limited reproduction range has been satisfactory for voice reproduction and for popular music. However, it has been most unsatisfactory for the reproduction of symphonic music.

Recent developments in audio sound engineering, such as FM radio and records made by new techniques and on improved materials have greatly expanded the frequency reproduction range. This expansion has extended from on the order of C. P. S. up to 10,000 or 12,000 C. P. S., and sometimes to the upper limit of the audio spectrum. Development of electrical components has kept pace, and even exceeded other components. Thus, electrical amplifiers can be and have been constructed with a substantially uniform response from a very few C. P. S., well below the audio range, to 50,000 C. P. S. or higher, thus accurately reproducing all of the partials or harmonics of symphonic music.

Electromagnetic pick-ups have been developed for use with phonograph records which have a satisfactory response over the entire audio frequency spectrum, as compared with the older pick-ups, typified by the crystal pick-ups which had a rather limited frequency response.

Thus, the weakest link in the audio chain at the present time is in the transducer, generally a loudspeaker for converting electrical oscillations into sound. Little trouble is experienced in reproducing the highest audio frequencies by the use of small loudspeakers having very little inertia. However, such small loudspeakers are physically incapable of moving a sufficient amount of air to transduce the low frequency tones. Accordingly, it has become common practice to utilize at least two loudspeakers in combination, one for the high frequencies and one for the low frequencies.

Even the larger loudspeakers are limited in low frequency reproduction, partly by the fact that loudspeakers must be held to a reasonable size for home-use, limitations being imposed both by the space available in a room and by the power available from an amplifier to drive the loudspeaker. Loudspeakers in common use are likely to resonate naturally at a frequency on the order of 50 C. P. S., and the response drops sharply below the resonant frequency. Furthermore, the loudspeakers in common use and commercially available do not have uniform response characteristics, but tend to peak `at certain frequencies with reduced efficiency between the peaks. As a result of such loudspeaker deficiencies, attention has been directed toward various types of enclosures for improving the coupling of the loudspeaker to the air and for generally flattening and extending the low frequency response and reproduction of loudspeakers.

Accordingly, it is the general object of this invention to provide an improved loudspeaker enclosure for extremely realistic reproduction of sound.

More particularly, it is an object of this invention to provide a loudspeaker enclosure combining the operating principles of the bass reflex, the Acoustic Labyrinth, the organ-pipe, and the horn.

It is a further object of this invention to provide a loudspeaker enclosure as contemplated by the foregoing object which requires no greater physical space than enclosures now in use.

Another object of this invention is to provide -a loudspeaker enclosure having an adjustable port for matching the characteristics of the loudspeaker and enclosure to those of the room in which the speaker and enclosure are located.

It is a further object of this invention to provide a loudspeaker enclosure having a plurality of resonating tubes of different lengths, and more particularly, to provide such a loudspeaker enclosure wherein the tubes are partially co-incident.

A still further object of this invention is to provide a loudspeaker enclosure incorporating acoustical filters to boost the response at pre-selected frequencies.

Other and further objects and advantages of the present invention will be apparent from the following description when taken in accordance with the accompanying drawings, wherein:

Fig. l is a perspective view of a loudspeaker and enclosure as constructed in accordance with the principles of my invention, the finish covering or veneer being omitted for clarity of illustration;

Fig. 2 is a fragmentary exploded perspective view of the enclosure;

Fig. 3 is a vertical sectional view through the rear or back portion of the enclosure as taken substantially along the line 3 3 in Fig. 5;

Fig. 4 is a similar vertical sectional View taken through the front portion of the enclosure substantially along the line 4 4 in Fig. 5;

Fig. 5 is a vertical sectional view through the enclosure at right angles to Figs. 3 and 4, and

Fig. 6 is a horizontal sectional View through the enclosure taken substantially along the line 6 6 in Fig. 5.

Referring now in greater particularity to the figures, there will be seen a loudspeaker enclosure generally identied by the numeral 10 comprising a front section 10a and a rear or back section 10b. The front section 10a includes a front panel l2 of generally rectangular configuration. This panel is provided with a circular opening 14 near the top thereof, and a loudspeaker 16 is mounted behind and preferably within the opening. Grille cloth might readily be placed across this opening in front of the loudspeaker in the finished article as is common practice, but it is omitted from the drawings for clarity of illustration. The front panel 12 further is provided with a port 18 adjacent the bottom. The port 18 is generally rectangular in conguration and is positioned close to the left side of the enclosure, being spaced slightly from the right side and having the upper right corner angled or bevelled as indicated at 20.

The front section 10a also comprises top and bottom walls 22a and 24a, a left side wall 26a, and a right side Wall 28a. An intermediate wall or panel 30 lying between the front and back sections will be considered with the front section inasmuch as it supports certain of the parts of the front section. This Wall 30 is of generally rectangular construction and lies parallel to the front panel 12 along the rear edges of the bottom wall 24a and the side walls 26a and 28a. The top edge of the intermediate panel 30 is terminated short of the top of the enclosure as indicated at 32, and is provided with a large notch 34 adjacent its top and near the left side thereof. This notch is generally/rectangular, but has tapering side walls, l.

being larger at the top edge of the panel;

A baille 36 lies between the front panel 12 and the intermediate panel 3i) and extends from the right side of the notch 34 generally diagonally down toward the lower right hand corner, the uppermost portion 38, and also the lowermost portion 4t) of the baille 36 being slightly deflected and substantially vertical in disposition. A deflector 42 extends across the front of the panel 30 from the left edge thereof to the baille 36. The deilector 42 is arranged at substantially a 45 angle relative to the panel 12 and the bottom wall 24a, and lies substantially directly behind the opening 18.

The intermediate panel 30 is provided at the lower right hand corner between the right side wall 28a and the baille 36 with an opening 44. Directly above this opening there is provided an acoustical illterV 46 completely filling the space between the side wall and baille and between the front panel and intermediate panel, being arranged at right angles to the side wall and to the front and rear panels. The filter 46 is of perforate or latticework construction, and is designed to reflect audio Vibrations on the order of 30 C. P. S., lower frequency vibrations passing through the filter.

The front section of the enclosure is completed by an island 4S of generally triangular construction. This island preferably is in the form of an isosceles triangle and mayV take the form of an equilateral triangle; On top of the island there is provided a shiftable baflle 50, this baille being held in place by a screw or bolt 51 extending through an elongated slot 53 in the baille.

The panel t) can be adjusted to the left or to the right by means of the bolt-inslot connection and is useful for varying the area between the island 48 and the baflle 36 and side wall 26a. The sound travels down past the island from the back of theloudspeaker 16, and the island acts as an expanding horn. The disposition of the panel 50 determines the area of the throat of the horn, and

thereby matches the speaker and enclosure to the room l.

in which they are placed.

An additional acoustical filter 52, this one being designed to reflect frequencies of 4() C. P. S. and higher, is mounted at the top of the panel 30 between the upper portion 38 of the baille 36 and the side wall 28a, and may be formed integral with the panel43tl. This particular disposition of the filter occurs only with the specific dimensions of my illustrative example, and it may be disposed horizontally inthe front section or in the back section depending upon the dimensions of the enclosure parts.

The rear section b of the enclosure comprises a rear or back panel V54 similar in outline to the front panel 12 and of imperforate construction. The back section ltlb further includes a top wall 2b, a left side wall 2619, a right side wall h and a Vbottom wall 24h respectively forming continuations of the correspondingly numbered parts bearing the suillx 61. The intermediate panel 36 is sandwiched between the corresponding wall sections as will beV obvious, and a suitable filler strip can be provided at the top where the intermediate wall or panel is terminated short of the top of the enclosure.

The back section 10b is provided with a pair of posts 56 extending forwardly from the rear wall S4 and bracing the intermediate wall or panel 3th adjacent the top edge 32 thereof.

There is also provided aresonant tube dividing wall 58 of generally hook shape and angled slightly as best may be seen in Figs. 2 and 3. A baille 6% extends diagonally upwardly from a position within the hook portion of the dividing wall 53 toward the upper right corner of the enclosure, being provided at its top edge with a vertical portion 62 aligned with the vertical portion 38 of the braille 36: in the front section. A 50 C. P. S. acoustical illter 64 extends from the baffle 60 over to the right side wall 28b, and also extends between the back wall 54 and the intermediate wall or panel 30.

The rear section is completed by an angularly disposed terminal wall 66 extending from a vertical wall portion 68 substantially aligned with the wall portion 40 in the front section to a position against the right side wall 28b adjacent the center thereof and immediately below the acoustical filter 64.

The main panels or walls of the enclosure as heretofore described are made of 5/8 in. plywood while the various dividers conveniently comprise one by six boards trimmed to the necessary size. The back section of the enclosure preferably also is provided with a pair of blocks Fil and 72 having curved inner faces and positioned beneath theY hook-shaped divider-wall 58 as will be apparent. The parts of the enclosure are assembled by means of glue and screws, and all joints are air-tight. For the sake of appearance the speaker opening 14 preferably would be covered with grille cloth as previously has been indicated, and the entire enclosure preferably would be covered with some sort of veneer or other covering for the sake of appearance.

Sound is transmitted directly from the front of the loudspeaker 16 as will be evident. Sound also is radiated from the back of the speaker along the path indicated at 74 by the dot-dash lines. This path extends on op posite sides of the island 48 and against the deilector 42, thereafter passing out through the port 1S. This action of the sound from the back of the speaker is generally similar to the well-known reflex enclosure. Due to the triangular shape of the island 48 the sound passageway increases in area moving along the island, and this gives rise to a short horn eifect. The panel 50 is movable from side to side as previously has been indicated for varying the area of the horn throat and for eifectively varying the area of the port 18.

There are two additional resonant paths for sound emanating from the back of the loudspeaker. The longer of these two paths is indicated by the dashed line 76. This path extends over the notched top of the intermediate panel 30 into the rear or back section and extends down between the sidewall 26h and the9 hooksnaped divider-wall 53. The path extends on around the hooked end of the divider-wall 58 and up between the baille 6i) and the side wall 28h as modiiied by the bale 66. The path 76 extends on over the top of the intermediate panel and into the front section where it extends down between the side wall 28a and the baille 36 to the opening 44 at the bottom of the intermediate panel. The path 76 then extends up again in a back section between the baille or wall 66 and the side wall 28h, this path being terminated at the junction of this baille and wall.

The remaining resonant path from the back of the speaker is indicated at 7S by the dotted line. This path also extends over the top of the intermediate panel 30 into the back section, and then down between the hook-shaped `divider-wall and the baille 60. The path 78 extends around the lower end of the baille 60 and up between the baille 60 and the side wall 28h as modifiedV by the baille 66, at this point being coincident with the path 76, and continuing co-incident with the path 76 to the termination thereof as will be evident from an inspection of Figs. 3 and 4.

These paths 76 and 78 are effectively resonant tubes operating according to the principles of the Acoustic Labyrinth and the organ-pipe. Since the path 76 passes around the outside of the hook-shaped divider wall 58 while the path 78 passes along the inside of this wall, the path 76 is substantially longer than the path 78. Accordingly, the tubes" in which these paths are disposed comprise resonant tubes of different lengths. it willV be observed that the cross sectional area of these tubes progressively decreases in area from the speaker toward the terminating end thereof in the same manner as an organ-pipe.

1t has been noted earlier that readily available loudspeakers generally resonate at 50 C. P. S. or above and have poor response below the resonant frequency. The acoustic lters 64, 52, and 46 respectively act to provide effective resonant tubes of proper lengths to resonate at these frequencies, thereby materially boosting the response below the resonant frequency of the loudspeaker, and extending the bass response of the loudlspeaker down substantially to the extreme bottom of the audio frequency spectrum.

The behaviour of the enclosure insofar as the paths 7o and 78 are concerned is similar to that of a closed pipe, thus requiring only 1A wave length for sound production. Thus, a good response down to 32 C. P. S. could be obtained by having the longer path 76 be at least 8 ft. in length. The path actually can be made to exceed 8 ft. without having the exterior dimensions of the enclosure increased to an impractical size, thus lowering the bass response considerably. With respect to the size, it will be noted that an enclosure constructed in accordance with the principles of this invention and having admirable performance is only 27 in. high, 16 in. across, and 12 in. in depth.

It appears that ratios involving halves or quarters between the lengths of the paths 76 and 78 should be avoided, and it has been found in practice that a ratio approximating 3:2 yields extremely good results, although practical considerations may require a lower ratio.

Various changes in structure will no doubt occur to those skilled in the art, and it will be appreciated that such changes in the illustrative embodiment herein shown and described do not depart from my invention but rather form a part thereof insofar as they fall within the spirit and scope of the appended claims.

l claim:

1. A loudspeaker enclosure comprising a front panel having means for mounting a loudspeaker, said panel having an opening therein displaced from said loudspeaker mounting means, means disposed internally of said enclosure forming a path in the interior of said enclosure between said speaker mounting means and the opening in said front panel, and means disposed adjacent said path defining means and positioned internally of said enclosure spaced from said opening for varying the area of said path to match a loudspeaker and said enclosure to the characteristics of a room.

2. A loudspeaker enclosure comprising a front panel having means for mounting a loudspeaker and also having a port therein, a panel spaced to the rear of said front panel, wall means joining said front panel and said other panel to complete said enclosure, said panels and said wall means defining a path between said speaker mounting means and said port, and restriction means disposed between said panels and spaced from both of said wall means substantially symmetrically bifurcating said path and providing a restriction in said path, said restriction means increasing the area of said path on the side of said restriction means toward said port, thereby to form a horn section in said enclosure.

3. A loudspeaker enclosure as set forth in claim 2 and further including means for varying the area of said restriction.

4. A loudspeaker enclosure comprising a front wall having means for mounting a loudspeaker and also having a port therein, a wall spaced rearwardly from said front wall, a plurality of walls extending between said front and said rearwardly spaced walls and forming a closed chamber therewith, said chamber including a path from said speaker and out through said port, and an island disposed in said chamber between said speaker mounting means and said port and engaging no more than two of said walls whereby to divide the sound path, `said island having a generally triangular outline with the base of the triangle oriented toward said speaker mounting means and the apex oriented toward said port whereby to form a horn section.

5. A loudspeaker enclosure as set forth in claim 4 and further including a member adjustable across the base of the triangle of said island for varying the area of the sound path past said island to match said enclosure and a speaker to the characteristics of a room.

6. A loudspeaker enclosure as set forth in claim 4 and further including a deecting panel angularly arranged behind said port for reflecting sound from a speaker carried by said speaker mounting means out through said ort. p 7. A loudspeaker enclosure as set forth in claim 4 and further including means providing a resonant chamber behind the first mentioned chamber and in communication therewith.

8. A loudspeaker enclosure as set forth in claim 7 and further including means dividing said resonant chamber into a plurality of resonant tubes of different lengths.

9. A loudspeaker enclosure as set forth in claim 8 and further including a plurality of acoustical filters disposed across said tubes.

10. A loudspeaker enclosure as set forth in claim 8 wherein said tubes are partly co-incident.

11. A loudspeaker enclosure comprising a generally rectangular closed box having speaker receiving means in the front thereof, and means within said box defining a plurality of resonant chambers of different lengths, said resonant chambers having entering ends in the vicinity of said speaker receiving means, and said resonant chambers being co-incident at their reflecting terminal ends.

12. A loudspeaker enclosure as set forth in claim 11 and further including acoustical filter means in said chambers providing resonance at a plurality of different frequencies.

13. A loudspeaker enclosure comprising a front panel, a rear panel, and an intermediate panel disposed in parallel, spaced apart relation, wall means encircling said panels and forming with the front and rear panels a generally rectangular box, the front panel being provided with an opening for receiving a loudspeaker, and also having a port opening therein, an island extending between said front and intermediate panels and having a generally triangular outline with the base oriented toward the loudspeaker receiving opening and the apex oriented toward the port opening, said intermediate panel having an interruption therein permitting communication between the spaces on opposite sides of the intermediate panel, transverse walls disposed between the intermediate and rear panels, and wall means between said front and intermediate panels, said wall means and said walls defining with the panels and with the encircling wall an acoustical labyrinth forming resonant tubes of different lengths.

14. A loudspeaker enclosure as set forth in claim 13 wherein certain of the walls and wall means are interrupted to render said resonant tubes co-incident adjacent their terminal ends.

1S. A loudspeaker enclosure as set forth in claim 13 and further including a member adjustable along the base of the triangle of said island for varying the area of the sound path past said island.

References Cited in the iile of this patent UNITED STATES PATENTS 1,727,105 Hawley Sept. 3, 1929 1,969,704 DAlton Aug. 7, 1934 2,203,875 Olson June 11, 1940 2,670,053 Dorus Feb. 23, 1954 FOREIGN PATENTS 641,718 Great Britain Aug. 16, 1950 OTHER REFERENCES Pub., Radio & Television News, Sept. 1951, pages 63, 144. 

